REmake was my first real experience with the series outside of seeing my cousins play the original, and it truly captivated me. Then RE4 came out and blew my tits off. Today, I can't really choose between the two of 'em, they're about equal for different reasons.
If held at gunpoint and forced to only choose one to play for the rest of my life? I'd say RE4. Reason being is it's such an incredibly streamlined, no-bullshit action game, even now, and it's packed with content without feeling tiresome or overbearing. I've played through it multiple times and will do so many more.